Abstract: The thermal element model of fiber coil was built based on the discrete mathematics formulae of the Shupe error in the fiber optic gyroscope (FOG). The transient thermal behavior and the steadystate thermal behavior were analyzed by this element model. According to these results, the reasons how the asymmetrical temperature field have an impact on bias error were found. The optimized structure of FOG shell, which has an inner of magnetically soft alloy and a outer of ultralumin , was designed, based on the analysis and emulation of the temperature field to decrease temperature grads of coil. The optimized thickness of the inner is 0.8 mm. The optimized thickness of the outer is 1.5 mm. It can improve the thermal symmetry of the fiber ring. The temperature changes of coil decreases by 1.8 ℃, and the difference in temperature of coil decreases by 0.68 ℃ in the temperaturefall period by experiments. Compared with the results of the experimentation, we approved the redesigned structure which can improve the temperature distributing and reduce the temperature spatiotemporal change rate of FOG coil.